1. Field of the Invention
The present invention relates to an apparatus and a method for changing a MultiCast and BroadCast Service (MCBCS) broadcasting channel in a Broadband Wireless Access (BWA) system. More particularly, the present invention relates to an apparatus and a method for presetting multiple MCBCS connections, as many as the number of channels in an MCBCS initialization process, to reduce a time delay associated with a channel change of a user.
2. Description of the Related Art
In the past, communication systems were developed with an emphasis on providing voice services. However, with the evolution of communication systems the emphasis has shifted to providing data services and various multimedia services as well as voice services. Voice oriented communication systems have not satisfied users' service needs because of their relatively narrow transmission bandwidths and expensive fees. Additionally, advances in the communication industry and users' increasing demand for Internet service has raised the need for communication systems that efficiently provide Internet services. In response to this demand, a Broadband Wireless Access (BWA) system is presented with enough capacity to meet the users' increasing demand for an efficiently provided Internet service.
The BWA system integrally supports not only voice services, but also multimedia application services such as various low-speed and high-speed data services and high-definition video services. The BWA system is a radio communication system capable of accessing a Public Switched Telephone Network (PSTN), a Public Switched Data Network (PSDN), the Internet, an International Mobile Telecommunications (IMT)-2000 network, and an Asynchronous Transfer Mode (ATM) network in a mobile or stationary environment based on radio medium using the frequency bands of 2 GHz, 5 GHz, 26 GHz, and 60 GHz, and supporting a channel transfer rate over 2 Megabits per second (Mbps). The BWA system may be classified as a broadband wireless subscriber network, a broadband mobile access network, and a high-speed wireless Local Area Network (LAN) based on the mobility of a terminal (stationary or mobile), the communication environment (indoor or outdoor), and the channel transfer rate.
The radio access scheme of the BWA system is standardized by the Institute of Electrical and Electronics Engineers (IEEE) 802.16 Working Group, which is an international standardization organization. Compared to a conventional radio technique for voice services, the IEEE 802.16 standard allows for the transfer of large amounts of data within a short time using a wide data bandwidth and allows all users to efficiently share and utilize the channel (or resource). Also, with Quality of Service (QoS) guaranteed, the users can enjoy services having different service qualities according to service characteristics.
An IEEE 802.16 system has a MultiCast and BroadCast Service (MCBCS) specification for providing multicast and broadcast services to a plurality of mobile terminals. The MCBCS specification allows for operation within the same multicast and broadcast service area by using different Connection IDentifiers (CIDs) or different Security Associations (SAs). A Multicast and Broadcast Service (MBS) zone (MBS_ZONE) indicates a region where broadcast and multicast services are operating by means of the CID and the SA. A Base Station (BS) broadcasts MBS zone information using a Downlink Channel Descriptor (DCD) message. Namely, the MBS zone is a BS group using the same CID and SA to transmit content.
As such, the 802.16 system can provide the MCBCS service to provide multicast and broadcast services. The MCBCS service is divided into a single-BS access and a multi-BS access mode of operation based on the service access method of a Mobile Station (MS). In the single-BS access mode of operation, the MS receives the MCBCS service from a single BS to which the MS is registered. In the multi-BS access mode of operation, the MS receives the MCBCS service from two or more BSs at the same time.
According to the multi-BS access mode of operation, when the MS travels into a region in which the current service cell overlaps with a neighbor cell, a signal of the neighbor cell acts as a signal gain through an RF combining process, rather than a noise by interference. This is the macro diversity effect. However, to acquire the macro diversity effect, a signal sent from the serving BS and a signal sent from the BS of the neighbor cell must be the same. Accordingly, to provide the MCBCS service, all of BSs in the MBS zone should transmit the signals at the same time.
The MCBCS service is expected to be one of the more vital services in establishing the prevalence of the mobile Internet. In a broadcasting service such as the MCBCS, one of the crucial service elements is a channel transition delay time. Herein, the channel transition delay time indicates a time taken for the user to change from a current channel to another channel, which starts when the user selects to change the channel and ends when the user views the requested channel.
According to a conventional channel transition method, the MS sends a channel transition request message to an MCBCS server for the channel change, and the MCBCS server triggers an Access Service Network-Gateway (ASN-GW) to control the BS to perform a Dynamic Service Deletion (DSD) process for the existing channel with the MS and to send a Multicast Connection ID (MCID) relating to the channel requested by the user to the MS through a Dynamic Service Add (DSA) process. Thus, the user can receive the broadcast in the changed channel. The conventional channel change method is subject to delay times, for example, the time taken for the MS to request the resource for sending a channel transition request message to the MCBCS server and to acquire a transmission right, the time taken to send the channel transition request message to the MCBCS server until a response is received, the time taken to establish the data path between the ASN-GW and the BS, and the time taken for the performance of the DSD and the DSA between the BS and the MS.
As discussed above, the conventional channel change method results in too much channel transition delay time. Therefore, what is needed is a method for reducing the channel transition delay time to provide the user with high-quality services.